Methods and compositions for cementing pipe in well bores

ABSTRACT

Methods and compositions for cementing pipe strings in well bores are provided. The compositions are basically comprised of a hydraulic cement, water, an in situ foam generating additive and a water-wetting foam stabilizing surfactant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to improved methods andcompositions for cementing pipe in well bores.

2. Description of the Prior Art

Hydraulic cement compositions are commonly utilized in primary sealingoperations whereby strings of pipe such as casing and liners are sealedin well bores. In performing primary cementing, a hydraulic cementcomposition is pumped into the annular space between the walls of thewell bore and the exterior surfaces of the pipe disposed therein. Thecement composition is permitted to set in the annular space therebyforming an annular sheath of hardened substantially impermeable cementtherein. The sheath physically supports and positions the pipe in thewell bore and is intended to bond the exterior surfaces of the pipe tothe walls of the well bore whereby the undesirable migration of fluidsbetween zones or formations penetrated by the well bore is prevented.

In a deep, high temperature well bore penetrating weak formations, thecementing of a pipe string in the well bore is often difficult andcharacterized by lost circulation during cementing and gas migrationthrough the resulting cement sheath. These problems are principallycaused by the use of a cement slurry having insufficient fluid losscontrol and using an aqueous spacer between the drilling fluid and thecement slurry which does not adequately remove drilling fluid from thepipe surfaces and the walls of the well bore. Further, at the hightemperatures encountered, when an oil based drilling fluid is used andthe aqueous spacer mixes with oil on the walls of the well bore,solidification of the mixture often results. The presence of drillingfluid and/or solidified oil-water mixtures in the well bore prevents thecement slurry from adequately bonding to the pipe and walls of the wellbore, and as a consequence, costly remedial cementing procedures arerequired.

Thus, there are needs for improved methods and compositions forcementing pipe strings in well bores drilled using oil based drillingfluids.

SUMMARY OF THE INVENTION

The present invention provides methods and compositions for cementingpipe in well bores which meet the needs described above and overcome thedeficiencies of the prior art. The methods of the invention basicallycomprise the steps of preparing a cement composition comprised ofhydraulic cement, water, an in situ foam generating additive and awater-wetting foam stabilizing surfactant; placing the cementcomposition in the annulus between the exterior surfaces of a pipestring and the walls of the well bore whereby the surfactant causesdrilling fluid in the well bore to be displaced therefrom and causes thepipe surfaces and walls of the well bore to be water-wetted whereby thecement composition will readily bond thereto; and then allowing thecement composition to foam and set in the annulus. The surfactant in thecement composition also facilitates and stabilizes the foaming of thecement composition which in turn helps prevent the migration of gas intoand through the cement composition.

The compositions of this invention are basically comprised of ahydraulic cement, water in an amount sufficient to form a pumpableslurry, an in situ foam generating additive and a water-wetting foamstabilizing surfactant. The in situ foam generating additive causes agas to be formed within the cement compositions which foams thecompositions prior to when they set and, as mentioned, the surfactant inthe cement compositions water wets the pipe and well bore surfaces,facilitates the formation of foam and stabilizes the foam.

It is, therefore, a general object of the present invention to provideimproved methods and compositions for cementing pipe strings in wellbores.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides improved methods and compositions forcementing a pipe string in a well bore, and particularly in such a wellbore which is deep, has a high bottom hole temperature, penetrates weakformations having high potential for gas flow into the well bore and wasdrilled using an oil based drilling fluid.

In accordance with the methods of the present invention, a cementcomposition is prepared comprised of hydraulic cement, water, an in situfoam generating additive and a water-wetting foam stabilizingsurfactant. The cement composition is placed in the annulus between theexterior surfaces of a pipe string and the walls of a well bore in whichthe pipe string is disposed, and the cement composition is allowed tofoam and set therein.

The in situ foam, generating additive in the cement composition producesa gas which foams the cement composition during and after its placementin the annulus. The water-wetting foam stabilizing surfactant in thecement composition facilitates the generation of the foam and stabilizesit. In addition, the surfactant functions to cause oil on the pipesurfaces and the walls of the well bore to be removed and the surfacesand walls to be made water-wet whereby good bonding between the cementcomposition and the surfaces and walls results.

A variety of hydraulic cements can be utilized in accordance with thepresent invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, pozzolanacements, gypsum cements, high alumina content cements, silica cementsand high alkalinity cements. Portland cements are generally preferredfor use in accordance with the present invention, and Portland cementsof the types defined and described in API Specification For MaterialsAnd Testing For Well Cements, API Specification 10, 5th Edition, datedJul. 1, 1990 of the American Petroleum Institute are particularlypreferred. API Portland cements include classes A, B, C, G and H, withAPI classes G and H being more preferred and class H being the mostpreferred.

The water utilized in the compositions of this invention can be from anysource provided it does not contain an excess of compounds thatadversely affect other components in the cement compositions. Forexample, the water can contain various salts such as sodium, potassium,calcium chloride or the like. Generally, the water is present in acement composition of this invention in an amount sufficient to form apumpable slurry. More particularly, the water is generally present inthe cement compositions of this invention in an amount in the range offrom about 35% to about 55% by weight of hydraulic cement therein (fromabout 4 to about 6.2 gallons per sack).

While various in situ foam generating additives can be utilized,aluminum powder or aluminum powder coated with a dispersing surfactantis preferably utilized. When added to an aqueous cement composition,aluminum powder delayedly generates hydrogen gas in the cementcomposition which causes it to foam during and after placement. The foamgenerating agent is included in the cement compositions of thisinvention in a general amount in the range of from about 0.1% to about1% by weight of hydraulic cement in the composition (about 0.1 poundsper sack to about 1 pound per sack), preferably in the range of fromabout 0.2% to about 0.7% (about 0.2 pounds per sack to about 0.66 poundsper sack), and more preferably about 0.5% (about 0.47 pounds per sack).

While various surfactants can be included in the cement compositions ofthe present invention for facilitating the removal of water based andoil based drilling fluids and filter cake from pipe and well bore andleaving them water wet surfaces and/or for facilitating and stabilizingthe in situ foam formed in the cement composition, a singlewater-wetting foam stabilizing surfactant is preferably utilized. Such asurfactant which is preferred for use in accordance with the presentinvention is an anionic surfactant comprised of an ethoxylated alkalimetal salt of an alkylpolyether sulfonic acid. The alkyl substituents ofthe ethoxylated alkylpolyether sulfonate preferably contain from about12 to about 15 carbon atoms and the alkylpolyether sulfonate ispreferably ethoxylated within the range of from about 2 moles to about50 moles of ethylene oxide per mole thereof. The ethoxylatedalkylpolyether sulfonate is dissolved in an aqueous solvent in an amountin the range of from about 20 parts to about 40 parts per 100 parts byweight of the solution. The most preferred water-wetting foamstabilizing surfactant for use in accordance with this invention iscomprised of a sodium alkylpolyether sulfonate ethoxylated with anaverage of about 15 moles of ethylene oxide per mole dissolved in anaqueous solvent in an amount of about 33 parts per 100 parts by weightof the solution. Such an aqueous surfactant solution is commerciallyavailable under the trade designation "STABILIZER 434C™" fromHalliburton Energy Services of Duncan, Okla. Other less preferredsurfactants which can be used include, but are not limited to,surfactants comprised of a sulfonated linear alcohol ethoxylate, anethoxylated nonyl phenol and a cocoamidobetaine.

The water-wetting and foam stabilizing surfactant is generally includedin a cement composition of this invention in an amount within the rangeof from about 0.5% to about 7% by weight of hydraulic cement in thecomposition (about 0.05 gallons per sack to about 0.75 gallons persack), preferably in an amount in the range of from about 0.5% to about5.7% (about 0.05 gallons per sack to about 0.6 gallons per sack), andmore preferably about 4.3% (about 0.45 gallons per sack).

A preferred cement composition of this invention for cementing a pipestring in a well bore drilled using an oil based drilling fluid iscomprised of a hydraulic cement, preferably Portland cement; water in anamount sufficient to form a pumpable slurry; an in situ foam generatingadditive, preferably aluminum powder, present in an amount in the rangeof from about 0.2% to about 0.7% by weight of hydraulic cement in thecomposition; and a water-wetting foam stabilizing surfactant, preferablythe above described sodium alkylpolyether sulfonate surfactant, presentin an amount in the range of from about 0.5% to about 5.7% by weight ofhydraulic cement in the composition.

A particularly preferred cement composition of this invention iscomprised of Portland API Class H cement; water present in an amount ofabout 40% by weight of hydraulic cement in the composition; aluminumpowder present in an amount of about 0.5% by weight of hydraulic cementin the composition; and a sodium alkylpolyether sulfonate ethoxylatedwith an average of about 15 moles of ethylene oxide per mole present inan amount of about 4.3% by weight of hydraulic cement in thecomposition.

The cement compositions of this invention preferably also include otheradditives commonly utilized in cement compositions and which are wellknown to those skilled in the art. For example, the compositions caninclude compressive strength retrogression control additives comprisedof powdered crystalline silica, one or more weighting materials, fluidloss control additives and set retarders. A preferred fluid loss controladditive is a graft lignin or lignite polymer commercially availableunder the trade designation "HALAD™ 413" from Halliburton EnergyServices of Duncan, Okla. The fluid loss control additive is generallyincluded in a cement composition of this invention in an amount in therange of from about 0.1% to about 1% by weight of hydraulic cement inthe composition. A preferred set retarding additive for use inaccordance with this invention is comprised of a copolymer of2-acrylamido-2-methylpropane sulfonic acid and acrylic acid commerciallyavailable under the trade designation "SCR-100™" from Halliburton EnergyServices and a set retarder intensifier comprised of tartaric acidcommercially available under the trade designation "HR-25™" fromHalliburton Energy Services.

As mentioned above, the methods of this invention are comprised of thesteps of preparing a cement composition of this invention, placing thecement composition in the annulus between the exterior surfaces of astring of pipe disposed in a well bore and the walls of the well boreand then allowing the cement composition to foam and set in the annulus.

As also mentioned above, because aqueous spacer fluids utilized betweenan oil based drilling fluid and a cement composition in a well boreoften cause the aqueous spacer fluid-oil based drilling fluid mixturesformed to solidify at high well bore temperatures, a spacer comprised ofan oil external-water internal emulsion is preferably utilized inaccordance with this invention. That is, an oil external-water internalemulsion spacer is placed in the annulus immediately preceding theplacement of the cement composition of this invention. The emulsionspacer fluid functions to separate the oil based drilling fluid from thecement composition, but it does not remove oil from the pipe surfacesand well bore walls. The removal of such oil is accomplished by thewater-wetting foam stabilizing surfactant included in the cementcompositions of the present invention which also leaves the pipe andwell bore wall surfaces water-wet whereby a good bond between the setcement composition and the pipe and well bore wall surfaces results.

In order to further illustrate the methods and compositions of thisinvention, the following example is given.

EXAMPLE

A 5" liner string was cemented in a 19,200' well bore drilled with an 18lb. oil (diesel) based drilling fluid. The bottom hole statictemperature of the well was 400° F. and the bottom hole circulatingtemperature was 339° F.

In performing the liner cementing job, a cement composition of thepresent invention was prepared, placed in the annulus between the wellbore and liner and allowed to foam and set therein. An oilexternal-water internal spacer was used ahead of the cement composition.The cement composition was comprised of Texas Lehigh API Class HPortland cement, fresh water present in an amount of about 41% by weightof cement in the composition (about 4.62 gallons per sack), an in situfoam generating additive comprised of aluminum powder present in anamount of about 0.5% by weight of cement in the composition (about 0.47pounds per sack) and a water-wetting foam stabilizing surfactantcomprised of an aqueous solution of an ethoxylated sodium alkylpolyethersulfonate (Halliburton "STABILIZER 434C™") present in an amount of about2.4% by weight of cement in the composition (about 0.25 gallons persack). In addition, a strength retrogression control additive comprisedof powdered crystalline silica was included in the composition in anamount of about 35% by weight of cement therein (about 37 pounds persack) along with a hematite weighting material present in an amount ofabout 32% by weight of cement (about 30 pounds per sack), a graft ligninor lignite polymer fluid loss control agent (Halliburton "HALAD™ 413")present in an amount of about 0.7% by weight of cement (about 0.66pounds per sack), a set retarder comprised of a copolymer of2-acrylamido-2-methylpropane sulfonic acid and acrylic acid (Halliburton"SCR-100™") present in an amount of about 1.6% by weight of cement(about 1.5 pounds per sack) and a set retarder intensifier comprised oftartaric acid (Halliburton "HR-25™") present in an amount of 0.8% byweight of cement (about 0.75 pounds per sack).

The above composition was run in the annulus between the liner and thewell bore until 200 sacks of the hydraulic cement had been used at whichtime additional cement without the surfactant was run to complete thejob.

The liner was found to have an exceptional bond log and it was the firstdeep, high temperature well in the area that the operator was able tocomplete without having to do considerable remedial cementing.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. A method of cementing a pipe string in a wellbore comprising the steps of:(a) preparing a cement compositioncomprised of hydraulic cement, water, an in situ foam generatingadditive and a water-wetting foam stabilizing surfactant; (b) placingsaid cement composition in the annulus between the exterior surfaces ofsaid pipe string and the walls of said well bore; and (c) allowing saidcement composition to foam and set in said annulus.
 2. The method ofclaim 1 wherein said cement is Portland cement.
 3. The method of claim 1wherein said water is present in said cement composition in an amount inthe range of from about 35% to about 55% by weight of hydraulic cementin said composition.
 4. The method of claim 1 wherein said in situ foamgenerating additive is aluminum powder.
 5. The method of claim 4 whereinsaid aluminum powder is present in said cement composition in an amountin the range of from about 0.1% to about 1% by weight of hydrauliccement in said composition.
 6. The method of claim 1 wherein saidwater-wetting foam stabilizing surfactant is comprised of a sodiumalkylpolyether sulfonate ethoxylated with an average of about 15 molesof ethylene oxide per mole.
 7. The method of claim 6 wherein saidwater-wetting foam stabilizing surfactant is present in said cementcomposition in an amount in the range of from about 0.5% to about 7% byweight of hydraulic cement in said composition.
 8. The method of claim 1which further comprises the step of placing a drilling fluid-cementcomposition spacer in said annulus immediately preceding the placementof said cement composition therein in accordance with step (b).
 9. Themethod of claim 8 wherein said well bore was drilled using an oil baseddrilling fluid and said spacer is comprised of an oil external-waterinternal emulsion.